An empty lifeboat that carried asylum seekers turned back by the Australian navy is seen docked at Pangandaran wharf in West Java, Indonesia.
Photograph: AFP/Getty Images

The Australian government has turned back 20 boats carrying 633 asylum seekers in the past 18 months, the immigration minister announced on Thursday.

Peter Dutton confirmed there had been 20 turnbacks since December 2013 but would not go into detail about when they occurred.

He framed the announcement as the successful prevention of asylum seeker deaths at sea and said that if those 20 boats had been allowed to reach Australia “200 or 2,000” could have followed.

“We have [more than] a year since we have had a successful people-smuggling operation and that is good news because we have had no reported deaths under Operation Sovereign Borders at sea and we have been able to stare down these evil people smugglers,” he told reporters in Sydney.

Dutton said the phrase “turnbacks” included scenarios such as assisted returns.

Dutton also used the announcement to attack the opposition, saying 50,000 people arrived on 800 boats under the previous Labor governments and the deputy leader, Tanya Plibersek, opposed the principle of turnbacks.

“You need to have the resolve to stare these people smugglers down and the Abbott government has had that resolve,” he said.

“If people smugglers see ventures getting to Australia successfully, that is a green light for the people smugglers to be back in business. That is why the government has the absolute resolve we have had from day one under Operation Sovereign Borders. It’s why it will remain because we are not going to allow the deaths at sea to recommence.”

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The most recent known turnback was a boat travelling from Vietnam carrying 46 asylum seekers. The turnback was confirmed in May. At that time the figure for the total number of turnbacks since September 2013 was put at 18 by Major General Andrew Bottrell, the commander of the government’s hardline asylum seeker policy.

Dutton said Australia worked on a bilateral basis with the Vietnamese government to return the asylum seekers.

“We have been able to stare down that venture and it’s a significant outcome and I want to praise the work of the Australian border force officers as well as those from defence because this was a very significant outcome,” he said.

Asked if there was an agreement in place with the Vietnamese government to send back boats, Dutton said there were negotiations on a case-by-case basis.

“We are working well with the Vietnamese government and I want to thank them for the effort and for their support in relation to returning these 46 Vietnamese to whom Australia had no protection,” he said.“Those people have arrived back safely.”

Asked how many boats have been turned back this year, Dutton said he was not going to break down the figure of 20.

Tony Abbott campaigned heavily on a slogan of “stop the boats” in the leadup to the 2013 election and the Liberal government has claimed success for the policy on numerous occasions.

The government has been secretive about its asylum seeker policy, rarely confirming turnbacks when they have happened.

There were allegations in May that navy officers had paid an asylum seeker boat bound for New Zealand to turn back to Indonesia. Many people have made the claims, including Indonesian police and asylum seekers on board, but the government has avoided directly responding to them.

“There’s really only one thing to say here, and that is that we’ve stopped the boats. That’s good for Australia, it’s good for Indonesia and it’s particularly good for all those who want to see a better world,” the prime minister said.